The present invention relates to a multilayer printed circuit board capable of preventing electromagnetic interference.
A high frequency current is applied to integrated circuits or large scale integrated circuits of the multilayer printed circuit board. The multilayer printed circuit board has a power layer, a ground layer and a signal layer. If the power layer and the ground layer form a large current loop circuits then a problem with the electromagnetic interference may be raised. In Japanese patent No 2734447, it is disclosed that in order to avoid this problem with the electromagnetic interference, a power de-coupling is emphasized, wherein the power layer comprises a wiring layer which includes an impedance-adding circuit. The impedance-adding circuit may be shaped in zigzag, crossing or spiral to avoid formation of the current loop. This power layer is sandwiched between underlying and overlying insulation layers which are made of an insulator mixed with a magnetic substance.
The above structure of the multilayer printed circuit board has the following problems.
The first problem is that when the integrated circuits or the large scale integrated circuits mounted on the multilayer printed circuit board are in operation, a high frequency current is applied to the power layer whereby the high frequency current applied to the power layer forms a large current loop which serves as a loop antenna which generates a radiation electromagnetic noise.
The second problem is that a current supplied from the power layer for switching the integrated circuits or the large scale integrated circuits causes variation in voltage of the power system comprising the power layer and the ground layer, whereby a stationary wave is caused and the power system serves as an antenna, so that the radiation electromagnetic noise with a frequency of the stationary wave is generated.
In Japanese laid-open patent publication No. 10-303563, a multilayer printed circuit board is disclosed. A single insulating layer is provided between the power layer and the ground layer. The single insulating layer include magnetic films which partially extend on selected regions of the insulating layer. The magnetic films are different in magnetic permeability, so that the insulating layer with the partially formed magnetic films serves as an electromagnetic shielding layer. Since the magnetic films are aligned in a single plane, it is possible for this conventional structure to attenuate the electromagnetic wave but only at a corresponding frequency to the frequency characteristic of the magnetic film. Accordingly, it is difficult for this conventional structure to attenuate the electromagnetic wave in a wide frequency range.
In Japanese laid-open patent publication No. 10-163636, it is also disclosed that magnetic sheet lamination structures are provided on both surfaces of a lamination of the power layer and the wiring layer. Each of the magnetic sheet lamination structures comprises a high magnetic permeability magnetic sheet and two low magnetic permeability magnetic sheets which sandwich the high magnetic permeability magnetic sheet. This magnetic sheet lamination structure is provided in order to increase the high frequency impedance with keeping the insulation between the power layer and the ground layer. The magnetic sheet lamination structure is not provided between the power layer and the ground layer which form a power system as a current loop. The magnetic sheet lamination structure is not provided in the current loop, for which reason the above structure having the magnetic sheet lamination structure is inapplicable to suppress the radiation electromagnetic noise.
Further, in Japanese laid-open patent publication No. 9-275251, various patterns of the conductive film applied to the multilayer printed circuit board are disclosed.
In Japanese laid-open patent publication No. 7-321463, a meshed interconnection layer applied for the multilayer printed circuit board are disclosed.
In Japanese laid-open patent publication No. 6-318650, plural stripe shaped power layers and ground layers applied for the multilayer printed circuit board are disclosed.
The foregoing conventional structures of the multilayer printed circuit boards are incapable of suppressing generation of a radiation electromagnetic noise and also incapable of attenuating the electromagnetic wave in the wide frequency range.
In the above circumstances, it had been required to develop a novel free from the above problem.
Accordingly, it is an object of the present invention to provide a novel multilayer printed circuit board free from the above problems.
It is a further object of the present invention to provide a novel multilayer printed circuit board capable of suppressing generation, in the wide frequency range, of a radiation electromagnetic noise from a power system comprising a power layer and a ground layer.
It is a still further object of the present invention to provide a novel multilayer printed circuit board capable of attenuating the electromagnetic wave in the wide frequency range.
It is yet a further object of the present invention to provide a novel multilayer printed circuit board capable of allowing a majority part of the high frequency current applied to the power layer to by-pass to a closest de-coupling capacitor so as to reduce, as many as possible, an effective high frequency current loop formed in the power system of the multilayer printed circuit board.
The present invention provides an inter-layer structure between a power layer and a ground layer. The inter-layer structure comprises an insulative magnetic layered structure which comprises at least two insulative magnetic substances which are different in frequency characteristic of complex magnetic permeability.
The other present invention provides an inter-layer structure between a power layer and a ground layer. The inter-layer structure comprises a dielectric layered structure which comprises at least two dielectric substances which are different in frequency characteristic of complex dielectric constant.
The above and other objects, features and advantages of the present invention will be apparent from the following descriptions.